Abrasive tool



June 12, 1956 F, G. PATRITO ABRASIVE TOOL Filed Aug. 23, 1954 IN VENTOR m mwa g m /M W 7 United States Patent ABRASIVE TOOL Francesco Giorgio Patrito, Turin, Italy Application August 23, 1954, Serial No. 451,326

2 Claims. (Cl. 51-204) This invention relates to an abrasive tool. The encasing of an abrasive tool is well known, generally in the form of a small plate or disc made of natural or artificial abrasive stone, with a casing adapted to wear away together with the stone itself.

Such casings have two distinct objects:

The first is that of protecting and holding the stone in a certain way so as to avoid abrading due to work pressure; and this is particularly useful when the work has to be done with thin stones which have in themselves little mechanical strength.

The second is that of providing a continual gauging means as the work proceeds, and specially to indicate the required dimensions for the workpiece in process of formation, and also of ensuring automatic stopping when that point is reached.

Technical literature includes numerous patents which are directed towards the above objects, or that resolve the problem partly, more or less totally, or more or less perfectly; such is the case, for instance, with the W. J. Bryant U. S. A. Patent 1,872,667.

In existing technical literature great importance has been given to the relation between the resistance and the wearing out of the stone in comparison with that of its casing. This shows clearly, according to the previous inventors, the necessity for such resistance to wear to be exactly the same for the stone and its casing, so that both of them have the same wear rate, with the result that the working surface of the stone and of its casing always remain on the same plane or level. Thus, the measuring or other gauging operation performed on the casing, correspond exactly with a similar operation executed on the stone.

The researches made by the applicant have demonstrated that the conditions realized according to those suppositions are not the most convenient for the work that the encased stones must perform.

According to the present invention we provide an abrasive tool comprising an abrasive stone which is encased, (exclusive of the working surface), in a casing having resistance to wear by abrasion appreciably less than that of the inserted abrasive stone, and having a low elastic compressibility. Examining the behaviour of an encased stone we note three fundamental cases:

First case: The casing has a resistance to wear slightly greater than that of the stone.

In such a case the stone tends to Wear away more rapidly than its casing, and for this reason as soon as the stone is worn out a little more than the casing, (a fact that depends on the elasticity of the casing itself),

the stone hardly operates on the Working surface. Thus only high friction, and great heating are incurred, having all the known consequences therefrom.

Second case: The casing presents a resistance to wear :equal to that of the stone.

This is the case in known arrangements, for example, in the Micromatic Italian Patent No. 448,762. In this Patented June 12, 1956 case the stone and its casing wear at the same rate, and, therefore, it is possible to measure on the nonabrasive part. The abnormal heating is not yet completely eliminated and as the biting edge on the stone is closely even with the casing plane its elfective sharpness is somewhat reduced.

Nevertheless, a type of tool of the kind referred to does exist; it is described in the D. T. Peden U. S. A. Patent, No. 2,467,094, in which it is stated that the casing, or covering, is formed of a resinous material which will wear at the same rate as the abrasive and which is lightly radially compressible under pressure. In such an arrangement the casing may extend infinitesimally beyond the working face of the abrasive stone when the pressure has ceased after a honing operation, thus preventing the working surface of the abrasive stone from coming into contact with the finished surface of the ground cylinder when the tool is removed. Thus the finished honed surface is not damaged, marred, or scratched, at the moment when the tool is taken away.

This type of tool behaves partly as though it belonged to the first case, and partly as though it belonged to the second case.

Third case: The covering presents a resistance to the wear less than that of the stone.

In this case the wear of the casing tends to be quicker than that of the stone, but as soon as the plane of the casing is lower than that of the stone (due also to the low compressibility of the latter) the pressure, together with the wear, tends to be transferred entirely to the stone itself. Therefore wear on casing and stone proceed at substantially the same rate, just as in the precedent case, but without reducing the biting of the stone.

It is, therefore, better to make the casing out of a material which will wear more rapidly than the stone.

This finding is limited by the fact that bodies more liable to wear out are in general less tenacious, and one must not forget that an important duty of the casing is that of protecting and bearing the stone. Naturally there is an intermediate point between those opposite requisites, a point that corresponds to the optimum of that complex tool; one will move from this optimum in practice, in either sense, according to the requirements of the case.

The materials utilisable for the encasing of the stone are numerous and include metals, enamels and plastic and resinous substances, Whether natural or artificial.

The researches of the applicant have shown that satisfactory materials are the phenolical resins. By adding loading substances, a mixture having the necessary degree of tenaciousness and resistance to wear can be obtained.

In any case, care should be taken that the casing or covering has sufficient elasticity or low compressibility to avoid conditions similar to those in the Peden patent. Such conditions have been found detrimental to a good performance of the tool in grinding or lapping operations.

An embodiment of the present invention will now be described by way of example, with reference to the accompanying drawing, in which:

Fig. 1 is a plan view of an abrasive tool according to the present invention:

Figs. 2 and 3 are sections along lines 11-11 and III- III of Fig. 1.

Figs. 4, 5 and 6 are enlarged sectional views illustrating respectively, the behaviour of tools according to the micromatic type, the Peden type, and according to the present invention.

Referring to the drawings, numeral 1 denotes an abrasive stone which may be natural or artificial.

Said stone is encased, being introduced core-like, in

3 a suitable mould made of synthetic phenolic resin (Bakelite) conveniently mixed up with loading substances.

The quality and quantity of the loading substances provides a bed 2 which offers a resistance to abrasion, and has a tenacity notatably below that of the stone 1, also a reduced elasticity and compressibility.

The casing covers the honing stone on five faces, leaving free only the working surface 3.

The working surface 3 of the honing stone is finished level with the casing on a curve that corresponds to the minimum diameter to which the tool is to work, if it is destined to work on internal cylindric surfaces, or instead, to the maximum diameter if destined to work on external surfaces.

The mixture may include an abrasive material, and the treatment of the material constituting the casing may be such that the casing itself will augment the abrasive power of the honing stone, allowing it to be regulated according to the requirements of the work to be done.

In this way the casing assumes a third functionthat of regulating'the degree of abrasive power of the whole tool, in addition, and often more important, that of strengthening and of gauging, which constitute the objects of the other known encasing devices.

I claim:

1. An encased abrasive tool comprising an abrasive stone and a casing enclosing the stone on all but its working surface, said casing being made of synthetic resin and a loading substance comprising abrasive material, whereby the resistance to abrasion and the tenacity of the casing are less than those of the encased stone.

2. An abrasive tool as set forth in claim 1, wherein the workin surface of the stone is finished level with the casing on a curve corresponding to the diameter of the surface of the object on which the tool is to work.

References Cited in the file of this patent UNITED STATES PATENTS 1,576,122 Webster Mar. 9, 1926 2,088,998 Merritt Aug. 3, 1937 2,265,377 Kline Dec. 9, 1941 2,552,485 Howard et al. May 8, 1951 2,675,654 Harris Apr. 20, 1954 

1. AN ENCASED ABRASIVE TOOL COMPRISING AN ABRASIVE STONE AND A CASING ENCLOSING THE STONE ON ALL BUT ITS WORKING SURFACE, SAID CASING BEING MADE OF SYNTHETIC RESIN AND A LOADING SUBSTANCE COMPRISING ABRASIVE MATERIAL, WHEREBY THE RESISTANCE TO ABRASION AND THE TENACITY OF THE CASING ARE LESS THAN THOSE OF THE ENCASED STONE. 